Golf Ball with Non-Circular Dimples Having Circular Arc-Shaped Outer Peripheral Edges

ABSTRACT

A golf ball provided with elliptical dimples. A golf ball provided with non-circular dimples, configured by forming the dimples in the surface of a sphere or of a pseudosphere which consists of a polyhedron. The dimples have a non-circular shape which has a major axis having a length at least 1.2 times greater than that of the minor axis of the shape, are each composed of a pair of circular arcs, and have a depth which causes the peripheral edges of the dimples to generate turbulence. The configuration reduces the separation width at the separation boundary to a level less than that of a golf ball having circular dimples, and this decreases the drag. The polyhedron can be substantially composed of triangles, pentagons, or hexagons.

TECHNICAL FIELD

The present invention relates to a golf ball with non-circular dimples which improve the aerodynamic properties of the golf ball.

BACKGROUND ART

Conventionally, it has been widely recognized that since a golf ball flies while rotating at a velocity of 20-70 msec, a golf ball having dimples with circular peripheral edges (simply called “circular” hereafter) has less drag than one without dimples in this velocity region, and a longer flight distance can be achieved by applying the same initial velocity. It is also widely known that large, circular dimples are preferable at low velocities and small, circular dimples are preferable at high velocities.

Therefore, in recent years, the shapes of dimples and the cross-sectional shapes of dimples have been variously investigated while keeping in mind the objective of increasing the lift-drag ratio (lift/drag), which has an effect on the flight distance of a golf ball. For example, a golf ball in which the peripheral edges of non-circular dimples are made to be triangular and are dispersed at prescribed spacing (Patent Document 1), a golf ball with an inverted cone-shaped cross section (Patent Document 2), and a golf ball in which the surface shape of dimples is made to be polygonal and ridge shapes are formed at the boundaries of adjacent dimples (Patent Document 3) have been proposed.

That is, for conventional golf balls, the predominant idea has been that dimples are essential in any event in order to increase the lift-drag ratio (lift/drag), which means that prescribed flat surfaces or ridge portions are necessary between adjacent dimples.

On the other hand, standards have been established for the weight, size, initial velocity, symmetry, and the like of golf balls, and a system of officially recognizing balls which conform to these standards (R&A Rules) so that the coefficient of restitution, which affects the initial velocity governing the flight distance, is restricted to a specific range. Therefore, three-piece and four-piece balls and materials have been variously developed as technologies for increasing the flight distance of golf balls within a prescribed range of the coefficient of restitution.

Prior Art Documents Patent Documents

Patent Document 1: U.S. Pat. No. 4,830,378 Specification

Patent Document 2: Japanese Unexamined Patent Application Publication H06-190082 Patent Document 3: Japanese Unexamined Patent Application Publication 2005-185341 DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

Therefore, as a result of dedicated research from an aerodynamic perspective while taking into consideration the fact that although the number of dimples, improvements in dimensions, and the number of layers of the ball such as three pieces or four pieces have been investigated since circular dimples were formed to improve balls with a restricted coefficient of restitution, there has been absolutely no progress in investigations of improvements from the perspective of actual aerodynamic properties, the present inventors obtained knowledge that shatters the conventional wisdom that circular dimples are optimal. That is, although it is necessary to form circular dimples on the surface of a golf ball to increase the lift and decrease the drag, with the knowledge of the present inventors, it was discovered that circular dimples on the surface of a conventional golf ball actually increase the drag due to increases in the amount of spin generated thereby for a golf ball which flies while rotating. As a result, although it is a phenomenon which frequently occurs with amateur hitting, when the striking surface of a club is not square with respect to the golf ball when struck, circular dimples give rise to a phenomenon in which the degree of hook or slice of the ball is likely to increase. On the other hand, the inventors arrived at the recognition that the matter of how to reduce air resistance during flight in the air while simultaneously improving the straightness of the trajectory of the ball is vital to the improvement of golf balls under the present circumstances in which, although the initial velocity of a ball is greatly affected by the coefficient of restitution of the ball, there are specific restrictions to the initial velocity of the ball.

Therefore, the first objective of the present invention is to provide a golf ball designed to be capable of increasing the lift-drag ratio (lift/drag) even if the amount of spin increases. The second objective is to provide a golf ball with excellent straightness of trajectory even if the striking surface of the club does not align squarely with the golf ball when struck.

Means for Solving the Problem

As a result of conducting dedicated research in order to solve the problem described above, the present inventors discovered from aerodynamic experiments and considerations that the conventional way of thinking is not necessarily correct. Specifically, as shown in FIG. 4(A), a golf ball which flies while rotating has a separation boundary in the vicinity of its maximum diameter, and drag is generated by the effect of vortices generated at the back of the golf ball from the separation boundary, so the ball is greatly affected by the separation width, which is the vertical width of the separation boundary. Therefore, the conventional way of thinking is to move the separation positions of these vortices to the back by forming circular dimples and to reduce the separation width and thus the drag in an attempt to achieve lift by the airflow speed difference above and below the golf ball due to the dimples, and the view that the formation of circular dimples is essential has been dominant. However, it was discovered that although the generation of vortices in the dimples cannot be avoided between a golf ball which flies while rotating and the peripheral air, when circular dimples are not formed (the present inventors formed a golf ball as a regular triangular polyhedron and formed grooves in the polyhedron ridge lines), the decrease in drag is substantial but sufficient lift cannot be achieved, and as a result, the flight distance required for a golf ball cannot be achieved.

The present invention, which was conceived based on new aerodynamic knowledge of the golf ball described above, is a golf ball having non-circular dimples in which the surface of a sphere is used to forma land part and a plurality of dimples are formed on the land part, wherein some or all of the plurality of dimples are non-spherical dimples surrounded by peripheral edges formed by a pair of circular arcs having the same or different curvatures extending on both sides of the ridge lines connecting the vertices of polygons inscribed in the sphere, and the major axis along the ridge lines of the inscribed polyhedron with non-circular dimples is at least 1.2 times greater than the minor axis orthogonal to the ridge lines.

It was discovered that if the non-circular dimples have ridges and a depth which generate turbulence at the peripheral edges, the vortices formed at the peripheral edge parts of the dimples are formed with a time difference, in contrast to circular dimples, so that the vortices that are generated flow along the peripheral edges of the non-circular dimples, and as a result, even if the amount of spin increases while the ball undergoes the lift due to the dimples, the separation width formed on the ball and thus the drag is reduced, as shown in FIG. 4(B), which leads to the improvement of the flight distance even at the same velocity (same coefficient of restitution). This phenomenon generates vertical vortices , and the flow of the vertical vortices of this ball in which the peripheral edges of the dimples are formed by circular arcs is not constant with respect to the traveling direction of the ball, in contrast to the case of circular dimples (with circular dimples, the direction of contact between the peripheral edges and air is always constant), so the vertical vortices generated at the peripheral edges do not stop at the peripheral edges of the dimples but rather flow along the peripheral edges. The present invention is functionally based on the fact that such a phenomenon occurs. Taking into consideration the symmetry of the ball, it is preferable for the peripheral edges of the dimples to be formed into elliptical shapes formed by a pair of circular arcs having the same curvature.

In the present invention, non-circular dimples surrounded by peripheral edges formed by a pair of circular arcs having the same or different curvatures extending along both sides of the entire ridge lines connecting the vertices of a polyhedron inscribed in a sphere are formed on the surface of the sphere (including pseudospheres composed of polyhedrons which are substantially similar to spheres). Using a triangular polyhedron as an example, a plurality of dimples having peripheral edges with a major axis DL (axis along the ridge lines of the non-circular dimples) of at least 1.2 times, preferably at least 2 to 10 times, and more preferably at least 2 to 5 times greater than the minor axis Ds orthogonal to the ridge lines of the non-circular dimples, as shown in FIG. 8, are formed. Here, each dimple consists of a pair of circular arcs 2 a and 2 b to form an elliptical shape if the curvatures of the circular arcs 2 a and 2 b are the same or a pseudo-elliptical shape if the curvatures of the circular arcs 2 a and 2 b are different. The depth of the non-circular dimples must be a depth required to generate turbulence when receiving the airflow of the periphery of the ball, as in the case of circular dimples, and the depth is ordinarily formed within a range of 0.2 to 0.5 mm.

The dimples of the present invention are preferably formed evenly over the entire surface of the ball, and assuming a triangular, pentagonal, or hexagonal polyhedron inscribed in the sphere, it is preferable to form the non-circular dimples so that the major axis of each dimple is positioned on each ridge line of the segmented face. In the case of a triangular polyhedron, a regular icosahedron shown in FIG. 5( a) is used as a base, and when each triangle is divided into two levels vertically and then split into four parts, as shown in FIG. 6( a), an 80-sided polyhedron is formed. When the triangle is divided into three levels and then split into nine parts, as shown in FIG. 6 (b), a 180-sided polyhedron is formed. When the triangle is divided into four levels and split into 16 parts, as shown in FIG. 6 (c), a 320-sided polyhedron is formed. Here, when forming non-spherical or elliptical dimples along each ridge line, 120 dimples are formed in the case of an 80-sided polyhedron, 270 dimples are formed in the case of a 180-sided polyhedron, and 480 dimples are formed in the case of a 320-sided polyhedron. The area occupied by the land part on each face changes depending on the minor axis diameter Ds of the dimples that are formed, but in order to improve the lift by adjusting the area occupied by the land part surrounded by the dimples in the case of a 80-sided polyhedron, in particular, it may be preferable to form at least one circular or polygonal dimple 3 on the land part surrounded by the non-circular dimples 2 of each face, as shown in FIG. 9.

If the polyhedron inscribed in the sphere is a pentagonal, hexagonal, or combined polyhedron consisting of pentagons and hexagons, the non-circular dimples described above may be formed along the ridge lines of each face, but taking the case of pentagons as an example, a regular dodecahedron is used as a base, as shown in FIG. 7 (a), and triangles are formed by line segments extending from the vertices of each pentagon face in the expanded view to the center of that face (FIG. 7 (b)), which makes it possible to manufacture a golf ball by forming non-circular dimples extending along the ridge lines of each triangle, as shown in FIG. 8.

The basic principle is that the non-circular dimples described above are formed across the entire length of each ridge line, but in order to improve the lift when dimples 2 are formed only in the central parts of the ridge lines and the land part is formed at the vertex portions, as shown in FIG. 10, the golf ball may be manufactured by forming circular or polygonal dimples 4 at the vertices of the polyhedron inscribed in the sphere.

That is, in the present invention, a polygonal polyhedron inscribed in a sphere is used as a foundation, and an inscribed polyhedron formed by further dividing each ridge line connecting the vertices or each face with triangles is presumed, wherein non-circular dimples surrounded by a pair of circular arcs are formed on the ridge lines connecting the vertices and used in place of conventional circular dimples. The area occupied by the land part (spherical surface) of the non-circular dimples is small, and if the lift is insufficient, the lift can be improved by forming circular or polygonal dimples on the remaining land part.

Effect of the Invention

With conventional circular dimples, the vortices formed at the peripheral edges tend to become stagnant, but with the present invention, the dimples on the ball surface are configured as non-circular dimples surrounded by a pair of circular arcs, so the vortices formed at the peripheral edges of the dimples are formed with a time difference and, as a result, flow along the elliptical peripheral edges so that they do not become stagnant. Accordingly, the drag is not increased even if the spin increases in comparison to a golf ball on which circular dimples are formed, and the flight distance improves as a result. Moreover, the straightness of trajectory is excellent since the air resistance, which causes the ball to hook or slice, is never increased.

BRIEF DESCRIPTION OF THE DRAWINGS

(FIG. 1) An oblique view showing the entire golf ball of a first embodiment of the present invention.

(FIG. 2) An oblique view of a second embodiment.

(FIG. 3) An oblique view of a third embodiment.

(FIG. 4) A conceptual diagram of a situation (A) resulting at the separation boundary of a golf ball with circular dimples and a situation (B) resulting at the separation boundary of the golf ball with circular dimples according to the present invention.

(FIG. 5) A cubic diagram (a) and an expanded view (b) of a regular icosahedron.

(FIG. 6) An explanatory view showing aspects in which each triangle of the icosahedron shown in FIG. 5 is divided into 4 parts (a), 9 parts (b), or 16 parts (c).

(FIG. 7) A cubic diagram (a) and an expanded view (b) of a regular icosahedron, and the expanded view shows an example in which a regular pentagon is divided.

(FIG. 8) An explanatory view showing a method of forming dimples with pairs of circular arcs when each face of the polyhedron has a triangular shape.

(FIG. 9) An explanatory view of a case in which circular dimples are distributed over a land part surrounded by non-circular dimples.

(FIG. 10) An explanatory view of a case in which circular dimples are distributed over a land part containing vertices when the non-circular dimples do not cover the entire lengths of the ridge lines of the inscribed polyhedron.

(FIG. 11) A schematic diagram of the second embodiment.

(FIG. 12) A cross-sectional view along line A-A in FIG. 11.

(FIG. 13) A cross-sectional view along line B-B in FIG. 11.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will be described in detail hereinafter based on the specific examples shown in the drawings. FIG. 1 shows a golf ball according to an embodiment of the present invention. In the drawing, 1 is a golf ball forming a sphere, wherein elliptical dimples 2 with a major axis (axis parallel to the ridge lines) 3.7 times as long as the minor axis (axis orthogonal to the ridge lines) are formed along the ridge lines connecting the vertices of a 180-sided triangular polyhedron inscribed in the sphere, and the dimple depth is 0.3 mm.

FIG. 2 is a golf ball 11 forming a sphere, wherein a major axis 1.9 times as long as the minor axis is formed along the ridge lines connecting the vertices of a 180-sided triangular polyhedron inscribed in a sphere, and elliptical dimples 12 with a depth of 0.3 mm are formed. FIG. 11 is a schematic line diagram of FIG. 2. FIG. 12 is an exploded cross-sectional view along line A-A in FIG. 11, and FIG. 13 is an exploded cross-sectional view along line B-B in FIG. 11.

FIG. 3 is a golf ball 21 forming a sphere, wherein a major axis 4.0 times as long as the minor axis is formed along the ridge lines formed by an imaginary 320-sided triangular polyhedron so as to form elliptical dimples 22 with a depth of 0.3 mm.

In the embodiment described above, the case of a sphere was used as an example, but elliptical dimples may also be formed on each ridge line of a triangular, pentagonal, or hexagonal polyhedron. Moreover, in the embodiment described above, elliptical dimples were formed on the ridge lines of 180- and 320-sided triangular polyhedrons inscribed in a sphere, but non-circular dimples may also be formed on the ridge lines of an 80-sided triangular polyhedron. That is, the gist of the present invention is that the peripheral edges of the dimples are formed as elliptical or non-circular shapes surrounded by pairs of circular arcs, and turbulence is generated at the peripheral edges with a time difference so that the vortices that are formed flow along the peripheral edges consisting of circular arcs. A person skilled in the art would be able to add variations and modifications without deviating from this gist. The present invention relates to the cover shape of a golf ball, so it goes without saying that the golf ball may be applied to the internal structures of golf balls such as a 4-piece structure in addition to 2-piece and 3-piece structures.

EXPLANATION OF REFERENCES

1, 11, 21 golf balls consisting of spheres

2, 12, 22 elliptical dimples 

1. A golf ball having non-circular dimples in which the surface of a sphere is used as a land part and a plurality of dimples are formed on the land part, wherein some or all of said plurality of dimples are non-spherical dimples surrounded by peripheral edges formed by a pair of circular arcs having the same or different curvatures extending on both sides of the ridge lines connecting the vertices of polygons inscribed in the sphere, and the major axis along the ridge lines of the inscribed polyhedron with non-circular dimples is at least 1.2 times greater than the minor axis orthogonal to the ridge lines.
 2. A golf ball according to claim 1 in which the outer shape of said dimples is an elliptical shape formed by a pair of circular arcs having the same curvature.
 3. A golf ball according to claim 1 in which the polyhedron inscribed in said sphere is a regular 80- to 320-sided triangular polyhedron and 120-480 non-circular dimples extending along each ridge line are formed.
 4. A golf ball according to claim 1 in which the polyhedron inscribed in said sphere is a regular 80-sided triangular polyhedron, wherein 120 non-circular dimples having peripheral edges are formed so as to extend along both sides of the ridge lines and at least one circular or polygonal dimple is formed in the land part surrounded by the non-circular dimples.
 5. A golf ball according to claim 1 in which the polyhedron inscribed in said sphere is an octagonal, hexagonal, or a combined polyhedron consisting of pentagons and hexagons, wherein triangles are formed by dividing each polygon face with line segments extending from the vertices to the center of the face, and non-circular dimples extending along the ridge lines of each triangle are formed.
 6. A golf ball according to claim 1 in which some or all of said plurality of dimples are non-circular dimples with peripheral edges consisting of pairs of circular arcs having the same or different curvatures extending along both sides of the central parts of ridge lines connecting the vertices of the polyhedron inscribed in the sphere forming the golf ball, wherein at least one circular or polygonal dimple is formed in the land part including the vertices of said inscribed polygons.
 7. A golf ball according to claim 1 in which the peripheral edges of said dimples have edge angles and depths so that vertical vortices are generated by the airflow received when the golf ball flies. 